Fused-ring and linking group effects of proton donors and acceptors on simple H-bonded liquid crystals

Two fused-ring structures, 6-decyloxy-2-naphthoic acid C₁₀ONA (3) and 6-dodecyloxyisoquinoline IS (8), were synthesized and utilized as proton donor and acceptor moieties to construct a series of simple mesogenic supramolecules. The other complementary hydrogen-bonded (H-bonded) moieties are benzoic acids, thiophenecarboxylic acid and pyridines containing different alkyl chain lengths connected by ether and ester linkages, i.e. 4-alkoxybenzoic acid C_nOBA (1), terephthalic acid monoalkyl ester C_nCOOBA (2), 2,5-thiophenedicarboxylic acid monodecyl ester C₁₀COOTHA (4), 4-alkoxypyridine C_nOP (6) and isonicotinic acid alkyl ester C_nCOOP (7). Several series of simple mesogenic supramolecular dimers were constructed from 1:1 molar ratios of proton donors (C_nOBA, C_nCOOBA, C₁₀ONA and C₁₀COOTHA) and proton acceptors (IS, C_nOP and C_nCOOP), though the proton acceptor C_nCOOP induced phase separation in all complexes. In order to investigate their fused-ring and linking group effects on the mesogenic properties of the H-bonded complexes, analogous simple supramolecular structures are compared. Supramolecular architecture and the distinct mesomorphism of these simple H-bonded liquid crystalline materials were confirmed by polarizing optical microscopy, DSC and powder X-ray diffraction experiments.